Make do with what you got.

[NO0C]

My project today: 150212-0120-B8 B&S Power Built™ 1150 engine (pressure washer application). I must have overtightened the muffler mounting bolts that I found loose when setting the overhead at one time, and both let loose (I hate aluminum threads) and they rattled out with all the vibration. I sure didn’t want to purchase a new cylinder head and didn’t want to spend between $25 and $40 for a HeliCoil kit that I would probably never use again. I had a 5/16-18 kit from another project (Tecumseh head bolts) a while back, so I decided to see if I could recoup some of its cost.

After inspecting the meat around the exhaust port, I decided to replace the M6 bolts with 5/16”, only a diameter difference of 0.078”. I did have to ream the muffler flange holes and gasket. All went well although the 5/16” hex bolts out of one of my treasure coffee cans could not be tightened due to interference from the weld between the flange and pipe and not being able to get a socket on them. I headed to Ace Hardware and picked up a couple stainless steel 5/16 X ¾” internal hex bolts and lock washers to take up the needed space and bingo everything fell into place. I would bet the farm that those will never loosen up and fall out. A happy camper in the Platte River Valley, I am, and only short a little time (worth nothing) and $2.59.

Thanks for listening.

[Arkie]

Couple things you might consider and check after you have run it awhile. Been their tried the stainless and got a surprise later when used on exhaust manifolds.

I've tried stainless steel bolts around hot exhaust manifolds (so as to prevent steel bolt seizing and rusting) and some of the stainless bolts will actually start stretching (more than steel) and break when subjected to the high heat, so recheck yours and be careful they don't twist off if they appear loose. Might want to consider using studs instead of a bolt. (use double jam nuts to install the stud)

I've installed studs into the head instead of bolts with good results when I have operating room for such. (Also try copper plus by permatex will act as a anti-sieze on manifold bolts or studs for later removal as it will take the heat and turn to a copper film) When you go to remove the exhaust later you have two options, of removal, the stud and nut comes out or just the nut and leaves the stud intact which is the desirable and no head thread damage.

Keep a heads up on the stainless bolts or you may find them broken off in the head due to stretch as some stainless bolts won't take high heat. If they appear loose do not attempt tightening or they may twist off.

Rusty, seized exhaust manifold bolts are a pain and even worse when they have limited access!!!!!!!!!!!!!!!!
I have a special little air hammer that I've rigged with a air regulator set at about 25# and button head punch to fast vibrate sting a rusted in exhaust bolt if it's seized in the block, works great to bust the internal rust.

Also it appears MAYBE that you have lock washers on the bolts which usually get hot and loose tension when subject to manifold heat and cause to bolts to become loose. I just use a flat steel washer or none at all.
Bottom line: recheck the torque after you have operated it awhile and every once in awhile to see how it's acting before you call it A-ok.

[NO0C]

Thanks for the tips Arkie. I’ll watch them closely. I debated whether to go with SS or not. I thought the SS bolts might be a better match with the SS HeliCoils, avoiding a dissimilar metal situation.

In this instance, studs are not an option as I would not be able to tighten the nuts due to the proximity of the muffler pipe to flange weld without adding washers to space the nut off the flange, plus getting a wrench on them is not possible without removing some of the nearby hardware, thus the reason I went with the internal hex bolts.

Thanks again.

[Fulltilt]

You really should remove the "socket head cap screws" and put some anti seize on them. They make a special compound for SS to SS, but regular stuff will work. Stainless fasteners tends to gall to each other.

[NO0C]

Thanks, I though of that and then 'senile citizenship' set in. Just as the poet laureate of Husker Nation says, 'Got Er Done' just minutes ago!

You really should remove the "socket head cap screws" and put some anti seize on them. They make a special compound for SS to SS, but regular stuff will work. Stainless fasteners tends to gall to each other.